Hydraulic power shovels which are widely used as construction machines, are generally constituted by a lower travelling truck body, an upper rotary body which is rotatably mounted on the lower truck body, and a working mechanism which is provided on a front portion of the upper rotary body.
The upper rotary body is largely constituted by a rotary frame in the form of a frame structure, an operator's cab which is mounted on a left-hand front portion of the rotary frame and internally provided with an operator's seat along with a number of operation control levers of the machine, a housing cover which is extended from right to a rear side of the cab and defining a machine chamber to accommodate an operating fluid tank, an engine, a hydraulic pump and other components on the rotary frame, and a counterweight attached to the rear end of the rotary frame as a balancing member relative to the working mechanism.
The operator's cab is constituted by a cab box, a box-like enclosure including a front side section, rear side section, left side section, right side section and top side or ceiling section, and a door which is attached to a center portion of its left side section and movable between a front closed position and a rear open position.
In connection with hydraulic power shovels, as disclosed in Japanese Patent Laid-Open Publication No. H1-198929, for example, there has been known in the art a within machine width revolving type or minimal radius revolving type hydraulic power shovel (hereinafter referred to as "small radius revolving type hydraulic power shovel) which is arranged to turn an upper rotary body within the width of the machine.
In the case of the prior art small radius revolving type hydraulic power shovel which is disclosed in Japanese Patent Laid-Open Publication No. H1-198929, the upper rotary body is arranged substantially in a circular shape when viewed from above, concentrically around the center of its rotation. By this arrangement, the upper rotary body of the hydraulic power shovel is prevented from hitting against an obstacle or a surrounding structure during its rotational movements.
In some cases, the door of the cab is left wide open on the rear side of the cab box during operation of the hydraulic power shovel, for ventilating purposes or when it becomes necessary for the operator to exchange words with someone outside the machine.
Therefore, according to the prior art hydraulic power shovel, in order to retain the cab door always within the radius of rotational movements of the upper rotary body even when it is left open as described above, the left side of the cab box which contains the door is located at an indented position inward of the radius of rotational movements, more particularly, at a position which is receded by a distance which corresponds to the dimension over which the door is projected laterally on the left side of the cab box when fully opened.
In the case of the above-mentioned conventional small radius revolving type hydraulic power shovel, due to location of the left side of the cab box in an indented position inward of the radius of rotational movements of the upper rotary body, the cab box is necessarily reduced in width, in other words, in spatial capacity between the right and left sides of the cab box.
Therefore, the dwelling space in the cab becomes narrowed down in the transverse direction to such a degree as to arouse oppressive feelings on the part of the operator, and degradations of the working environment and maneuverability of various operation control levers and pedals.